diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 0cdf0b283..8eec94fcb 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -5,12 +5,12 @@
 
 #include "nixexpr.hh"
 #include "symbol-table.hh"
+#include "hash.hh"
 
 
 namespace nix {
 
 
-class Hash;
 class EvalState;
 struct Env;
 struct Value;